CPM refers to the cost per 1,000 ad impressions, a widely used yardstick to measure the price of digital advertising campaigns.

“This chart shows that during [the] general election period, Trump campaign paid slightly higher CPM prices on most days rather than lower as has been reported,” Bosworth noted.

He publicised the information following an article in Wiredbased on a statement from Trump’s digital director in 2016, Brad Parscale. The report suggested that the Trump campaign got a better deal on Facebook advertising than Clinton, arguing that Facebook rewarded the more divisive ads from the current president.

Bosworth explained that if this had happened, Trump ads would have seen a lower CPM. He said: “Prices depend on factors like size of audience and campaign objective. These campaigns had different strategies. Given the recent discussion about pricing we’re putting this out to clear up any confusion.”

After some discussion we've decided to share the CPM comparison on Trump campaign ads vs. Clinton campaign ads. This chart shows that during general election period, Trump campaign paid slightly higher CPM prices on most days rather than lower as has been reported. pic.twitter.com/u0qgUQ02qM

Parscale had said that Trump was the “perfect candidate for Facebook”, which caused major controversy and sparked the need for Bosworth to disclose the figures. Although it shows that higher rates were paid overall by the Trump campaign, Wirednoted that some important elements of the story have yet to be addressed.

Much of the anger from the general public arose from the alleged prioritisation of provocative ads by Facebook, an aspect of the events that was not clarified by Bosworth’s tweets. Also not apparent from the recent disclosure is the pricing of types of messages and targeting. An ad targeted at customised audiences would see a higher CPM than a more general ad and the chart doesn’t show what each of the campaigns would have had to fork out for an identical ad buy.

A more complicated story

When it comes down to it, the marked difference in how both campaigns used Facebook as a tool makes it extremely difficult to make accurate comparisons at a granular level.

As AdAge pointed out: “The cost per thousand impressions is not the only metric that determines success. The numbers, for instance, don’t take into account the amount of free impressions each side received from people sharing the ads after seeing them in their Facebook news feeds.

“It’s also likely that Trump’s team made better use of targeting tools that could drive up rates but offer more effective outcomes, while Clinton’s ads, though less expensive, were less relevant.”

Facebook is launching a tool later this year to make its advertising rules more transparent to users and customers alike.